1. Field of the Invention
The present invention relates to a die apparatus used for blanking a thin plate, and a method for blanking the thin plate.
2. Description of the Related Art
Pressing equipment generally includes a pressing die (die apparatus) having an upper die with a punch fixed and held, and a lower die with a die fixed and held, the lower die arranged just under the upper die, and is constructed so that a component with a predetermined shape can be pressed or blanked by relatively moving (upwardly and downwardly moving) the upper die and the lower die in a vertical direction.
The pressing die further includes a stripper plate arranged between the upper die and the lower die, and a stripper holder for holding the stripper plate. Normally, the stripper plate and the stripper holder are collectively called a stripper.
In the case of use, by downwardly moving the upper die, a workpiece (for example, an electromagnetic steel plate) is pressed by the stripper and the die, and the plural punches are guided by the stripper plate, and the workpiece is pressed or blanked.
A press load of the stripper for pressing the workpiece described above is applied by an elastic force of a spring (spring) as described in, for example, JP-A-59-166328 as Patent Reference 1.
Since quality of blanking of the workpiece depends on variations in the press load of the stripper at the time of blanking, a spring is arranged so that a knockout load of a stripper 80 is applied to the inside (center side of a workpiece 82) of a stripper plate 81 in order to make a press load of the stripper 80 uniform as shown in FIG. 6. FIG. 6 also indicates a stripper holder 83 and a die 84 (lower die).
However, a press structure of the conventional stripper has the following problem.
In the case of air punching at the time of feeding a material etc., as shown in FIG. 7, since the workpiece 82 is not present between the stripper 80 and the die 84, a gap 85 is formed and when the stripper 80 is subjected to a press load, the stripper 80 flexes in the vicinity of the bottom dead center. Accordingly, a position of a punch 86 guided by the stripper 80 is displaced and also, the punch 86 bites into the die 84 (the punch 86 interferes with an inner surface of the die 84).
Consequently, chipping (a phenomenon in which an edged tool chips) occurs in both of the punch 86 and the die 84 due to the displacement of the position of the punch 86 and the bite into the die 84.
Particularly, the problem described above is remarkable in a step of forming a caulking protrusion (also called BEND).
Since the caulking protrusion is formed by half blanking the workpiece without completely blanking the workpiece, it is difficult to control the bottom dead center of the punch.
Hence, as described in JP-A-6-238361 as Patent Reference 2, a punch insert formed on the base side of the punch is butted on a back surface of the stripper plate in order to always maintain the position of the bottom dead center of the punch used for forming the caulking protrusion constant.
Patent Reference 1: JP-A-59-166328
Patent Reference 2: JP-A-6-238361